1. Field of the Invention
The present invention relates generally to an apparatus and method for supporting a preforms and more particularly to an apparatus and method that can accommodate preforms having different dimensions.
2. Related Art
A preform support device is used to secure a preform in place so that the preform can be moved. Preform support devices can be coupled together in an endless chain for transferring preforms. A preform transfer chain consisting of such devices is found especially in plants for manufacturing containers, such as bottles, flasks or the like, made of a plastic, especially a thermoplastic such as polyethylene terephthalate (PET). More particularly, a transfer chain formed in this way is used to move the preforms from a charging station up to and through a heating oven (tunnel oven) in which the perform material is heated for subsequent molding, by a blow molding or stretch-blow molding process, into a large container (either the final container or an intermediate container). Such a transfer chain is described in U.S. Pat. No. 5,316,127 which is incorporated herein by reference.
A preform support device that can be coupled together one after another to form the transfer chain is described in U.S. Pat. No. 5,857,562 which is incorporated herein by reference. Such a preform support device is shown in FIG. 1. The device 1 includes a hollow body fixed to a mounting plate 2. The body 4 consist of two parts, an upper and a lower part which are fixed in the mounting plate 2, for example, by screwing from above and below the mounting plate. A rod 5 is supported so as to rotate freely in the hollow body 4. Sleeves are provided inside the hollow body 4 to guide the rod. The rod 5 is capable of being moved axially. A spring 6 is provided to return the rod 5 to its starting position. At its free end, the rod 5 is provided with a gripping head 7 designed to be removably or releasably fastened to the open end of a preform 8. The gripping head 7 can be frictionally pressed into the opening of a preform 8.
The gripping head 7 is typically sized to be substantially the same size as or slightly larger than the interior diameter of the opening of the preform. The gripping head 7 is then compressed and secured within the open end of the preform. It is important that the size of the gripping head and the size of the opening in the preform match each other. Otherwise, the gripping head may be to large and will not fit into the opening of the preform or the gripping head may be to small and will not frictionally engage the preform. Thus, each gripping head can only be used with a particular size preform or preforms having openings within a very limited range, typically no variation of 0.006 inches and beyond.
Consequently, in order to use the prior art preform support device or preform transfer chain for preforms of different sizes, the production line must be shut down so that the appropriately sized preform support device for the different sized preforms can be installed. Obviously, this causes a significant delay in production time and a corresponding increase in production cost. Moreover, many different types of preform support devices are required to fit the many different types and sizes of bottles that may be manufactured. Therefore, there is a need for a preform support device than can accommodate multiple size preforms and that eliminates the need for changing over the production line.